Gap arthroplasty

The gap arthroplasty aims to reduce the rate of re-ankylosis by increasing the distance from the cut surface of the ascendent ramus to the cranial base.

A temporalis muscle interposition flap will help prevent reankylosis and to some extent compensate the loss of height of the mandibular ramus.

Although the temporalis muscle interposition flap is the most widely used for this purpose, other materials eg. dermal grafts, fat and silicon blocks have also been used.

A superiorly extended preauricular approach (Al-Kayat approach) is used to expose the entire ankylosed temporomandibular joint.

In the case of ankylosis, an ostectomy of the condyle head (condylectomy) is made with a bur or saw leaving a gap of 15 mm or more between the surfaces of the condyle and the skull base

The remaining condylar stump is reshaped with a bur to achieve a rounded contour.

In the case of pseudoankylosis a resection of the affected soft tissues including osteotomy of the condylar head is carried out using a burr or saw. A gap of 15 mm or more is created.

The remaining condylar stump is reshaped with a bur to achieve a rounded contour.

If the fractured condylar head is dislocated out of the fossa or severely comminuted, and the resulting interarticular gap is larger than 15 mm, then no further resection or osteotomies are required.

At this point, if an inter incisal opening of less than 35 mm is measured intraoperatively, a decision to perform uni- or bi-lateral coronoidectomies is made.

This procedure is performed via the transoral approach to the coronoid process. This is in principle a modification of the transoral approach to the condyle, where the coronoid process is exposed instead of the condyle.

An Al-Kayat incision is made starting in the pretragal area extending superiorly to the temporalis region. The vertical third of the incision is carried anteriorly in the format of a hockey stick to gain adequate exposure. The depth of the incision goes to the superficial temporalis muscle fascia.

Depending on the amount of muscle necessary to reach and cover the glenoid fossa, parallel incisions are made through the temporalis muscle. The length of the flap depends of the thickness needed to fill the interarticular gap.

Starting from the top edge of the temporalis muscle, the flap is elevated down to the root of the arch to ensure that it is long enough to be rotated to reach and coat the glenoid fossa.

The flap is transferred into its preplanned position by rotating it lateral to the zygomatic arch to cover the glenoid fossa. Great care is taken not to create undue torsion or tension within the pedicle.

The flap is sutured to the medial aspect of the remaining condylar neck and it is verified that the muscle remains on top of the condylar stump during mandibular function.

The defect produced in the temporalis muscle is checked for hemostasis. Approximating sutures are placed as needed. The incision is then closed in layers with deep absorbable sutures and 5-0 permanent suture for the skin closure.

Prior to wound closure, a Penrose or suction drain may be used to prevent dead space and the formation of hematoma.

If MMF screws are used intraoperatively, they are usually removed at the conclusion of surgery. Arch bars may be maintained postoperatively for functional therapy.

Postoperative x-rays are taken within the first days after surgery.

It is imperative that the occlusal relationship and mandibular function be assessed early and on a regular basis. The patient is evaluated at 1 week to verify the occlusion and to assure adequate performance of functional rehabilitation exercises.

If a malocclusion is detected, the surgeon must ascertain its etiology (using the appropriate imaging technique). If the malocclusion is secondary to surgical edema or muscle splinting, training elastics will be beneficial. The lightest elastics possible are used for guidance, because active motion of the mandible is desirable. Patients should be shown how to place and remove the elastics using a hand mirror.

If the malocclusion is secondary to a bony problem due to incorrect bone alignment (mal reduction) or hardware failure or displacement, elastic training will be of no benefit. The patient must return to the operating room for revision surgery. A slight malocclusion can be corrected by orthodontics or dental adjustments with the help of a dentist.

The frequency of follow-up will largely be based on the findings of the 1 week appointment. Typically, if the patient is doing well at 1 week, they will not be seen for 2 more weeks. The necessity and frequency of future appointments will be based upon the findings from this appointment.

Postoperatively, patients will have to follow three basic instructions:

1. Diet:
The patient can consume liquids and semiliquids for the first couple of weeks and then advanced to more solid foods as tolerated and recommended by the surgeon.

2. Oral hygiene
Patients with extraoral approaches are not compromised in their routine oral hygiene measures and should continue with their daily schedule.
Patients with intraoral wounds must be instructed in appropriate oral hygiene procedures. The presence of the arch-bars and any elastics makes this a more difficult procedure than normal. A soft toothbrush (dipping in warm water makes it softer) should be used to clean the surfaces of the teeth and arch-bars. Any elastics are removed for oral hygiene procedures. Chlorhexidine oral rinses should be prescribed and used at least three times each day to help sanitize the mouth. For larger debris, a 1:1 mixture of hydrogen peroxide/chlorhexidine can be used. The bubbling action of the hydrogen peroxide helps remove debris. A Waterpik® or similar device is a very useful tool to help remove debris from the wires. If a Waterpik is used, care should be taken not to direct the jet stream directly over intraoral incisions as this may lead to wound dehiscence. The assistance of a dental hygienist may be helpful.

3. Physiotherapy
Patients are instructed in physical therapy maneuvers to restore mandibular excursions. This includes maximum jaw opening, right and left lateral excursions, and protrusive excursions of the mandible, as well as assistance from a physiotherapist if required. They should perform these exercises several times a day.